Heating plate device



R. s. GOLQDTHWAITE HEATING PLATE DEV IO E Fild Jan. 16, 1937zdkllllllllllllllll llllll ri ATTORNEYS.

Patented 4, 1939 UNITED STATES HEATING PLATE DEVICE Robert S.Goldthwaite,

Marion, Ind., assignor to Rutenber Electric Company, Marion, Ind., a

corporation Application January 16, 1937, Serial No. 120,937

1 Claim.

This invention relates to an electric heating plate.

By the terminology plate, the same does not necessarily apply to a planestructure.

The chief object of the invention is to simplify the construction of aheating device, commonly known as an electric heating plate, and tostrengthen the same.

Another object of the invention is to produce a construction of theaforesaid character in a relatively simple, economical and expeditiousmanner.

The chief feature of the invention consists in the formation of aheating plate of the character briefly set forth hereinbefore, and morefully set forth hereinafter and in a manner hereinafter to be more fullydescribed.

The full nature of the invention will be more fully understood from theaccompanying drawing and the following description and claim:

In the drawing,

Fig. 1 is a top plan view of an electric heating plate shown circular inoutline and parts being diagrammatically indicated therein.

Fig. 2 is an end elevation of the plate shown in Fig. 1, parts beingbroken away to show the same and other parts in central section.

Fig. 3 is an enlarged transverse section through one form of heatingplate structure.

Fig. 4 is a similar view of a modified form of heating plate structure.

Fig. 5 is an enlarged sectional view through a plurality of adjacentportions of the same strips embodied in the invention, following thewinding operation.

Fig. 6 is a similar view of the same parts following the insulating stepand previous to the application of the cover or supporting platethereto.

In the drawing indicates a metal heating plate, H a shell, and I2 a backplate. As shown in Fig. 2, the back plate rests on the flange Ila of theshell and the adjacent edges of the shell and top or cover plate aresuitably secured together by press-fitting, welding, or the like, as 45indicated at Illa.

In Fig. 3 similar numerals increased by one hundred, indicate like orsimilar parts and in this figure the plate H0 is welded to the flangelllb of the shell HI having the spaced and inwardly directed flange Illawhich supports the back plate I I2.

In Fig. 4, similar numerals of the two hundred series indicate likeparts. In this form, the top plate 2 It has a downwardly directed grooveforming portion ZlUa adapted to nest the outwardly directed flange 2| lbof the shell 2H having the inwardly directed lower flange 2i la, uponwhich rests the back plate 2l2. In the chamber thus formed,substantially all of the space not occupied by the members hereinafterto be described, is filled with a suitable heat and electricalinsulation, such as mineral wool, indicated in Fig. 2 by the numeral I 3and in Fig. 3 by the numeral H3 and in Fig. 4 by the numeral 2l3.

In Fig. 2 of the drawing, there is illustrated 10 a metallic ribbon I 4which is arranged in scroll formation, as shown diagrammatically inFig. 1. The same is suitably secured as at Iii-that is, its adjacentlateral edge is welded, brazed, or the like, to the cover or vesselsupporting plate It). In the channel formed between adjacent portions [4is positioned a heating element in the form of a strip of resistancematerial 5. The width of the strip [6 as shown clearly in Fig. 2, isless than the width of the metal strip [4. In other words, the heatingelement or strip I6 is nested between adjacent portions of the heatconducting strip M which also serves as a reenforcement for the cover orheating plate Ill. The strip l4 serves to confine the heat and localizeit so that it is imparted to the strip 14 and thence directly conductedto the plate 1!], except that portion of the heat which rises directlyupwardly toward the plate Ill. The heat which is directed downwardly isprevented, to a greater or less degree, from being transmitted to plate12 by the mineral wool insulation 13, or the like.

In one form of the invention portions I4 may be cast integral with theplate I0 and the heating strip 16 when suitably enveloped by electricalinsulation, may be nested in the groove or channel formed by theaforesaid.

The inner end of the scroll arranged heating strip includes an angularextension I! which projects through an aperture IS in an insulatingmember [9 mounted in the aperture 20 in the plate l2.

Suitably secured to the plate l2 as at 2| is a bracket 22 that mounts ascrew bolt 23 bearing a nut 24 thereon. The screw bolt 23 is insulatedfrom the bracket by suitable insulation washers 25. One currentconducting line may be clamped between the nut 24 and the metal washer26. The lead wire portion ll of the heating strip is clamped between thewashers 2! and 28.

A similar type of terminal structure is associated with the opposite endof the heating wire, the lead-in portion being indicated by the numeral29, with the offset portion thereof by the numeral 30 and the sameextends beneath the 55 plate to the end of the strip It in the outerchannel or groove, as indicated at 3I. The lead-in strip 29 is suitablyinsulated from the back plate I2 as at 32.

In Fig. 3 of the drawing, the reenforcing and thermal conducting metalstrip is indicated by the numeral H4. The adjacent edge of the same isconnected as at H5 to the cover or vessel supporting plate I I0.Positioned in the groove 01 channel between adjacent portions of thestrip H4, is the electric heating strip H6. The strips lI4I I6 are ofdissimilar width. The two strips are superimposed upon each other with astrip of insulation I35 and another strip of insulation I35. The entiresuperposed strip arrangement is then Wound on a suitable mandrel andthus the electric heating strip is electrically insulated from thereenforcing strip. As shown clearly in Fig. 3, when the strips areassociated in wound relation, they are tightly associated together andform a unit with the channel, as it were, between adjacent-portions ofthe strip I I4and above the upper and lateral edge of the heating stripH6.

The electrical insulating strips I35 originally may be metallicmagnesium ribbon, subsequently oxidized for use.

Before securing the heat conducting portions IM to the cover or vesselsupporting plate I I0, this channel may be filled with magnesium oxideproviding insulation I36 between the cover plate and the electricheating strip. The cover plate, as will be apparent, protects theelectric heating strip from water, or the like, from a vessel, such as acoffee pot, et cetera, overflowing and shorting out sections of theheating unit. It will be apparent when the portions I I4 are secured tothe cover I IEI that the heating element and the unit as an entiretyis'rigidly held together by the cover plate.

In Fig. i a slightly modified form of the invention is illustrated. Inthis form of the invention, the strip 2M again is of greater width thanthe heating strip 2I6. However, in this instance, the thermal conductingmetal strip 2 I I is provided with a groove or channel 2M0. adapted tonest, partially or completely, as desired, depending upon the depth ofthe channel or groove 2!, the electric heating strip 2I6. .Interposedbetween the electric heating strip 2I6 and the metal'strip 2 are stripsof insulating material 235.

The four strips are simultaneously wound upon a mandrel and since theinsulation strips are of lesser width than the heat conducting andreenforcing strip, the structure when assembled is such that relativetransverse movement of the heating strip with respect to the heatconducting strip is prevented. Thereupon the heating unit may have thelateral and upper edge of the strip 2M suitablysecured or united tothecover plate 2 Ill as at 2I5.

The insulation strips in each of the before The heating'strip again isillustrated as being of a less width than the thermal conducting stripand the insulation strips are each illustrated as being of greater widththan the heating strip but of less width than the thermal conductingstrip.

After being wound into a heating unit, the insulation strips 335 mayhave their channel exposed portions 3350. directed inwardly and havetheir ends contact as at 33517. sufiicient insulation to prevent theelectric heating strip from contacting the cover plate and shorting out.If desired, additional insulation, as indicated at 336, may be supplied,this being in the form of the magnesium oxide or any equivalentmaterial. Following the formation of the unit, as shown in Fig. 6, theheat conducting strip 3M is suitably secured to the cover or supportplate. I

One form'of insulating strip isof mica material. The resultingconstruction, how so ever formed, forms a heating plate in which heat isgenerated in the ribbon wire or heating strip and by reag son of itsshape, provides a greater amount of surface per unit of cross sectionand in this way, the heating strip per unit of length has a greatersurface for heat emanation. Likewise, this construction provides thatall points of the surface of the heating strip are within a relativelyshort distance of heat conducting metal so that the heat may be readilyconducted away from the source to the cover or vessel supporting plate.This results in the temperature of the heating strip or wire being keptrelatively low and this adds to the length of life of the wire. Sincethe heat generated by the same is concentrated on the cover or vesselsupporting plate, the elflciency of this type of heating device is muchgreater than similar heating devices, heretofore employed in the art.

One suitable form of uniting the thermal conducting strip to the coveror plate is by a copper brazing process which results in a highlyefficient thermal bond as well as a mechanical bond. In place of themineral wool, previously described as useful for filling the chamber ofthe heating device and designated by numerals I3, H3 and 2I3 in Figs. 2,3 and 4, respectively, the same may be of asbestos character or apulverized form of other suitable material.

One problem inherent in the construction disclosed herein, is that it isdesired to position the heating strip as close to the cover or plate aspossible. Hence, danger of shorting the electric heating strip by itsslippage and contacting the cover plate must be positively prevented byany one of the disclosures set forth herein or one of equivalentcharacter.

Inasmuch as the insulation material filling the chamber of the devicehas considerable thickness below the heating portion of the device, moreespecially the heating unit, shorting between the electric heating stripand the back plate is not a problem and hence, no special provision forinsulation-other than that shown or described is deemed necessary.

-As indicated-at I36 and 336 in Figs. 3 and 6, respectively, magnesiumoxide powder may be placed in these grooves, the cover plate superposedupon the thermal conducting strip and then the two united in any'desiredand suitable manner.

Increased efficiencyiof the device is also obtained by making theinterior surface of the back plate of non-tarnishing character by eithermaking the plate of non-tarnishing material and mechanically polishingthe same or by coating the interior face of the back plate with suitablepro- This forms a tective material so that its surface is bright andwill remain so. Such a bright or polished surface, therefore, Willreflect any and all heat rays directed upon it from the heating strip H6upwardly and away from it and thus toward the cover plate.

The terminology adjacent non-continuous portions is intended to refer toportions in the same strip which are adjacent each other and spacedapart as in a spiral or scroll by the dis tance between adjacentportions in a radial plane as distinguished for adjacent portions inimmediate continuity.

While the invention has been described in great detail in the foregoingspecification, the same is to be considered as illustrative and notrestrictive in character. Various modifications have been illustratedand described herein and these modifications as Well as others suggestedherein and others Which will readily suggest themselves to personsskilled in this art, are considered to be Within the broad scope of theinvention, reference being had to the appended claim.

The invention claimed is:

An electric heating device including, a vessel or like supporting heattransmitting plate of comparatively thin section in thickness and ofgreat area, means supporting said cover plate at its peripheral edge, anelongated continuous electric heating strip beneath the plate and ofbare metallic resistance type ribbon of rectangular like section andWound on edge with one of its edges adjacent and substantially parallelto the cover plate, a corresponding heat conducting metal strip injuxtaposition to the heating strip, rigid with the cover forreenforcement thereof against Warpage and correspondingly Wound andhaving a corresponding edge in direct thermal contact with the cover forthermal conductivity, means electrically insulating the heating stripfrom the cover and the juxtapositioned reen-- forcing strip, the twostrips being of scroll outline, the heat conducting strip including agroove in one side face thereof for laterally nesting the heating striptherein for locating purposes, the insulation means being at both sidesof the heating strip, the strips and insulation being coiled into acompact mass, the heat conducting strip including a projecting portionat one side of the groove for rigid connection to the cover, and a heatdeflecting plate beneath the heating and metal strips and spaced fromthe heating strip and associated with the cover supporting means.

ROBERT S. GOLDTHWAITE.

